Current methods for sampling and evaluating air concentrations of gases and vapors involve the use of pumps or direct-reading instruments. The sampling media used on pumps ultimately gives a time-weighted average result; fluctuations in concentrations are smoothed out resulting in poor temporal resolution of chemical concentrations. Although direct-reading instruments do not suffer from the temporal resolution problem, both methods are essentially point samplers and give poor spatial resolution of concentrations. Currently there are no methods which can give both good spatial and good temporal resolutions of chemical concentrations in an area. This application proposes a method, using an optical remote sensing network combined with computed tomography, to determine the concentration distribution of a gas or vapor in a room. It is a departure from currently used air samplers, and does not suffer from the spatial and temporal resolution drawbacks. The aims of the research are: 1. to develop and test a theoretical design for a remote sensing/computed tomography system and, 2. to construct and test a prototype remote sensing system. The theoretical design will be evaluated by performing computer simulations of ideal and non-ideal sampling conditions: detector noise, blocked rays, and fewer rays. The prototype optical remote sensing system will then be constructed, based upon the developed theoretical design, inside a wind-tunnel used to simulate a room. An open-path infrared optical remote sensing detector will be used in the wind-tunnel to detect different concentration distributions of the tracer gas, sulfur hexafluoride. The measurements will be validated with an electron capture detector. Mathematical algorithms developed in the theoretical part of the work will be used to perform the reconstructions. Successful completion of this research will result in the development of an operating system for measuring gas and vapor concentration distributions that is non-invasive and operates in real-time. This system could be used for routine monitoring of chemical vapors in a workplace, evaluation of ventilation systems by using tracer gases or monitoring airflow of chemicals, detection of leaks from an operation, and emergency evaluation of spills.